The lubricating fluid (synovial fluid) reduces friction between the articular cartilage and other tissues in a joint and lubricates and cushions the bone and tissue components of the joint during movement. If the lubricating fluid is negatively affected and/or the joint articular cartilage usually covering the bone of the joint is damaged, in most cases due to older age and/or continuing extensive or abnormal strain on human or mammal joints (e.g. knee joint, hip joint), this can result in a degenerative joint disease (also known as osteoarthritis) characterized by a painful inflammation of the joint. Upon pathological reduction and change of composition of the lubricating fluid within the joint space, which consists of the articulating surfaces of the adjacent bones with the joint being stabilized and encompassed by the joint capsule and the synovial membrane, the lubricating fluid can no longer perform its usual task, i.e. lubrication of joint areas and shock absorption, together with the articular cartilage.
If the articular cartilage is severely damaged due to osteoarthritis or the like and/or the synovial fluid is reduced or altered in its composition reducing its potential to lower friction within the joint, the articulating surfaces are subjected to high friction and increased wear causing a painful inflammation of the joint. This can result in serious restraints of movement, especially in walking and standing, which further augment degenerative processes of the joint. Degenerative joint disease is highly prevalent in the western world, with this disease being one of the leading causes for chronic disability in Europe and the US.
Patients with osteoarthritis require a regular long term treatment by which lubricating fluid is introduced into the affected joint, which, on the one hand, re-stores the physiological functionality of the damaged joint as far as possible and, on the other hand, involves as little extra stress as possible—both physical and psychological—for the patient.
A known standard therapy is periodical extracorporeal injection of synthetic lubricating fluid into the joint space by a syringe in order to substitute the absent physiological lubricating fluid. In such conventional treatment it is inconvenient for the patient to deliver the lubricating fluid at regular time intervals through the skin and the joint capsule into the joint by way of a syringe. Also, this may cause injuries to the skin and the joint capsule, which increases the risk of severe infections of the delicate joint tissues. Therefor, an injection may not be performed more often than every 6 months.
Artificial joints have been an important part restoring the functionality of the natural joints of patients suffering from joint osteoarthritis and fractured and damaged joints. Among the most successful material combinations is the ceramic and polymer combination called the Charnley type joint. This prosthesis type however, has a limited life span of 15-20 years due to wear of the polymer component. The particles created from the polymer wear triggers a macrophage reaction which has been found affects the fixation of the prosthesis in the femoral bone and in worst cases makes the prosthesis come loose. Loosening of prosthesis is the number one reason for having to redo hip joint surgery. Since the polymer material of the prosthetic Acetabular cup is relatively soft, the material need to be of considerable thickness for being stiff enough, for enabling fixation of the cup and for resisting the wear from the contact with the prosthetic caput femur. The use of harder materials in the Acetabular cup have the disadvantages of creating sounds when walking which propagates out of the body, furthermore harder material do not create the desired elastic properties which is needed for reduce strains placed on the fixations of the prosthetic parts against the natural bone tissue.